During the loading or unloading of a parked truck, trailer, or other vehicle at a loading dock, it is important from a safety standpoint to secure the truck in place so as to prevent accidental movement away from the loading dock while personnel and material handling equipment (e.g., dollies, carts, fork lifts, etc.) are transporting material between the truck and loading dock. Inadvertent or premature separation of the truck from the loading dock can create a hazardous situation since a gap then exits between the truck and the loading dock.
In accordance with governmental regulations, a safety bar, commonly referred to as an ICC (Interstate Commerce Commission) bar or rear-impact guard, is mounted to the rear end of most trucks. The purpose of the ICC bar is to prevent a low profile vehicle from passing under the read end of the truck when involved in a rear end collision. An additional use of the ICC bar is to restrain or secure a parked truck to a loading dock by engaging the ICC bar of the truck. Such vehicle restraints are disclosed, for example, in U.S. Pat. Nos. 4,282,621 (Anthony et al.), 4,373,847 (Hipp et al.), 4,379,354 (Hahn et al.), 4,443,150 (Hahn et al.), 4,472,099 (Hahn et al.), 4,560,315 (Hahn), and 4,605,353 (Hahn et al.).
As shown in FIGS. 1-4 of the drawings, one style of conventional vehicle restraint 30 includes a carriage assembly 40 which is adjustably mounted for substantially vertical movement with respect to a front wall 16 of a loading dock 10, a generally hook-shaped restraining member 50 which is housed within the carriage assembly 40 and is pivotably attached thereto via a shaft (not shown), and a motor (not shown) for selectively rotating the shaft and the attached restraining member 50. As is customary, the restraining member 50 includes a shank portion 51 with a proximal end 52, a leg portion 53 with a free distal end 54, and a throat portion 56 disposed between the shank portion 51 and the leg portion 53. As shown in FIGS. 2-4, the leg portion 53 of the restraining member 50 extends at an angle from the shank portion 51 to form the hook-like shape. In order to protect the motor, the shaft is provided with a slip clutch (not shown) which allows the shaft to rotate against the motor when an external force above a predetermined magnitude and tending to rotate the restraining member 50 (i.e., a "torque" 60) is exerted on the restraining member 50. Also, the carriage assembly 40 is biased to assume a first vertical position, but may be moved downwardly into a lower vertical position when an external force (such as that provided by the ICC bar 22 of a truck 20 which is moving backwardly towards the loading dock 10) is exerted on an exposed cam surface 42 of the carriage assembly 40.
In order to releasably secured a parked truck 20 to the loading dock 10, the restraining member 50 is rotatable between an operative (or vehicle-locking) position and a stored (or vehicle-release) position. In the operative position, the restraining member 50 protrudes outwardly and upwardly from the carriage assembly 40, preferably to a position wherein the distal end 54 of the restraining member 50 extends up and over the restrained ICC bar 22 of a truck 20 so as to effectively trap the ICC bar 22 in the throat portion 56 of the restraining member 50, as shown, for example, in FIG. 2. When the restraining member 50 interlockingly engages the ICC bar 22 in this way, the ICC bar 22 is, in effect, "trapped" or "hooked" by the restraining member 50. That is, when the ICC bar 22 moves away from the loading dock 10, the restraining member 50 is pulled into tighter engagement with the ICC bar 22, thus providing a restraint to prevent the truck from inadvertently moving away from the loading dock 10. In the stored position, on the other hand, the restraining member 50 is fully retracted within the carriage assembly 40, and the truck 20 is free move away from the loading dock 10.
Certain circumstances, however, may prevent the restraining member 50 from interlockingly engaging the ICC bar 22 in this manner. For example, if the ICC bar 22 is located above the first vertical position of the carriage assembly 40 such that the distal end 54 (and not the throat portion 56) of the restraining member 50 engages the front vertical surface 25 of the ICC bar 22, as shown in FIG. 3 (instead of extending up and over this surface, as shown in FIG. 2), movement of the truck 20 away from the loading dock 10 subjects the restraining member 50 to an external force 60 which tends to rotate the restraining member 50 in a direction toward the stored position. Because of the slip clutch, such a force 60 may cause the restraining member 50 to rotate toward the stored position and cause the restraining member 50 to become fully disengaged from the ICC bar 22 of the truck 20. Should this occur, the truck 20, of course, would no longer be secured to the loading dock 10.
Similarly, if a cover plate 24 is mounted in front of the ICC bar 22, as shown in FIG. 4, interlocking engagement between the restraining member 50 and the ICC bar 22 of the truck 20 is prevented because the distal end 54 of the restraining member 50 cannot get up and over the ICC bar 22. Although the distal end 54 of the restraining member 50 engages (i.e., merely touches) the cover plate 24, movement of the truck 20 away from the loading dock 10 subjects the restraining member 50 to an external force 60 which tends to rotate the restraining member 50 out of the operative position. If the distal end 54 fails to bite into the cover plate 24, the truck 20 could be inadvertently moved or driven away from the loading dock 10.